Berg J.M., Tymoczko J.L., Stryer L. Biochemistry

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4 pN = 8.8 × 10

-13

pounds. The weight of a single motor domain is 100,000 g mol

-1

(6.023 × 10

molecules mol

-1

) =

1.7 × 10

-19

g = 7.6 × 10

-23

pounds. Thus, a motor domain can lift (8.8 × 10

-13

/7.6 × 10

-23

) = 1.2 × 10

times its

weight.

See question

After death, the ratio of ADP to ATP increases rapidly. In the ADP form, myosin motor domains bind tightly to

actin. Myosin-actin interactions are possible because the drop in ATP concentration also allows the calcium

concentration to rise, clearing the blockage of actin by tropomyosin through the action of the troponin complex.

See question

Above its critical concentration, ATP-actin will polymerize. The ATP will hydrolyze through time to form ADP-

actin, which has a higher critical concentration. Thus, if the initial subunit concentration is between the critical

concentrations of ATP-actin and ADP-actin, filaments will form initially and then disappear on ATP hydrolysis.

See question

Actin monomers bind and hydrolyze ATP and are in somewhat different conformations, depending on the identity of

the bound nucleotide. Thus, nucleotide binding and then hydrolysis by actin filaments might change actin's length,

shape, or rigidity.

See question

The first (a) should behave like conventional kinesin and move toward the plus end of microtubules, whereas the

second (b) should behave like ncd and move toward the minus end.

See question

A one-base step is approximately 3.4 Å = 3.4 × 10

-4

µm. If a stoichiometry of one molecule of ATP per step is

assumed, this distance corresponds to a velocity of 0.017 µm s

-1

. Kinesin moves at a velocity of 6400 Å per second,

or 0.64 µm s

-1

See question

A protonmotive force across the plasma membrane is necessary to drive the flagellar motor. Under conditions of

starvation, this protonmotive force is depleted. In acidic solution, the pH difference across the membrane is

sufficient to power the motor.

See question

10.

(a) The force is 6π(0.01 g cm

-1

)(0.0002 cm)(0.00006 cm s

-1

) = 2.3 × 10

-9

dyne. (b) The work performed is (2.3

× 10

-9

dyne)(0.00006 cm) = 1.4 × 10

-13

erg. (c) On the basis of a ∆ G value of -12 kcal mol

-1

(50 kJ mol

-1

) under

typical cellular conditions, the energy available is 8.3 × 10

-13

erg per molecule. In 1 second, 80 molecules of ATP

are hydrolyzed, corresponding to 6.6 × 10

-11

erg. Thus, a single kinesin motor provides more than enough free

energy to power the transport of micrometer-size cargoes at micrometer-per-second velocities.

See question

11.

The spacing between identical subunits on microtubules is 8 nm. Thus, a kinesin with a step size that is not a

multiple of 8 nm would have to be able to bind on more than one type of site on the microtubule surface.

See question

12.

KIF1A must be tethered to an additional microtubule-binding element that retains an attachment to the microtubule

when the motor domain releases.

See question

13.

Protons still flow from outside to inside the cell. Each proton might pass into the outer half-channel of one MotA-

MotB complex, bind to the MS ring, rotate clockwise, and pass into the inner half-channel of the neighboring

MotA-MotB complex.

See question

14.

At a high concentration of calcium ion, calcium binds to calmodulin. In turn, calmodulin binds to and activates a

protein kinase that phosphorylates myosin light chains. At low calcium concentration, the light chains are

dephosphorylated by a calcium-independent phosphatase.

See question

15.

(a) The value of k

cat

is approximately 13 molecules per second, whereas the K

value for ATP is approximately

12 µM. (b) The step size is approximately (380 - 120)/7 = 37 nm. (c) The step size is very large, which is consistent

with the presence of six light-chain-binding sites and, hence, very long lever arms. The rate of ADP release is

essentially identical with the overall k

cat

; so ADP release is rate limiting, which suggests that both motor domains

can bind to sites 37 nm apart simultaneously. ADP release from the hindmost domain allows ATP to bind, leading

to actin release and lever-arm motion.

See question

Common Abbreviations in Biochemistry

A adenine

ACP acyl carrier protein

ADP adenosine diphosphate

Ala alanine

AMP adenosine monophosphate

cAMP cyclic AMP

Arg arginine

Asn asparagine

Asp aspartate

ATP adenosine triphosphate

ATPase adenosine triphosphatase

C cytosine

CDP cytidine diphosphate

CMP cytidine monophosphate

CoA coenzyme A

CoQ coenzyme Q (ubiquinone)

CTP cytidine triphosphate

cAMP adenosine 3

,5 -cyclic monophosphate

cGMP guanosine 3

,5 -cyclic monophosphate

Cys cysteine

Cyt cytochrome

d 2

-deoxyribo-

DNA deoxyribonucleic acid

cDNA complementary DNA

DNAse deoxyribonuclease

EcoRI EcoRI restriction endonuclease

EF elongation factor

FAD flavin adenine dinucleotide (oxidized form)

FADH

flavin adenine dinucleotide (reduced form)

fMet formylmethionine

FMN flavin mononucleotide (oxidized form)

FMNH

flavin mononucleotide (reduced form)

G guanine

GDP guanosine diphosphate

Gln glutamine

Glu glutamate

Gly glycine

GMP guanosine monophosphate

cGMP cyclic GMP

GSH reduced glutathione

GSSG oxidized glutathione

GTP guanosine triphosphate

GTPase guanosine triphosphatase

Hb hemoglobin

HDL high-density lipoprotein

HGPRT hypoxanthine-guanine phosphoribosyl-transferase

His histidine

Hyp hydroxyproline

IgG immunoglobulin G

Ile isoleucine

inositol 1,4,5,-trisphosphate

ITP inosine triphosphate

LDL low-density lipoprotein

Leu leucine

Lys lysine

Met methionine

NAD

nicotinamide adenine dinucleotide (oxidized form)

NADH nicotinamide adenine dinucleotide (reduced form)

NADP

nicotinamide adenine dinucleotide phosphate (oxidized form)

NADPH nicotinamide adenine dinucleotide phosphate (reduced form)

PFK phosphofructokinase

Phe phenylalanine

inorganic orthophosphate

PLP pyridoxal phosphate

inorganic pyrophosphate

Pro proline

PRPP 5-phosphoribosyl-1-pyrophosphate

Q ubiquinone (or plastoquinone)

ubiquinol (or plastoquinol)

RNA ribonucleic acid

mRNA messenger RNA

rRNA ribosomal RNA

scRNA small cytoplasmic RNA

snRNA small nuclear RNA

tRNA transfer RNA

RNAse ribonuclease

Ser serine

T thymine

Thr threonine

TPP thiamine pyrophosphate

Trp tryptophan

TTP thymidine triphosphate

Tyr tyrosine

U uracil

UDP uridine diphosphate

UDP-galactose uridine diphosphate galactose

UDP-glucose uridine diphosphate glucose

UMP uridine monophosphate

UTP uridine triphosphate

Val valine

VLDL very low density lipoprotein